1. Field of the Invention
Embodiments of the present invention generally relate to a lift mechanism for controlling the position of a substrate support in a processing chamber.
2. Description of the Related Art
Many semiconductor processing operations, for example, chemical vapor deposition, physical vapor deposition and etch, among others, are performed in a vacuum environment. Typically, a substrate is positioned on a movable substrate support disposed within a processing chamber. The elevation of the substrate support is controlled by a lift mechanism so that the substrate may be disposed at a lower position within the processing chamber to facilitate substrate transfer and an elevated position that typically enhances substrate processing. As the spacing between the top of the processing chamber and the substrate seated on the substrate support may be 200 mils or closer when in the elevated position, the parallelism between the top of the processing chamber and the substrate support is a major attribute in maintaining process uniformity across the width of the substrate and ensuring process repeatability between substrates. For example, if one edge of the substrate is closer to the top of the processing chamber than another edge of the substrate, gases flowing between the substrates and the top of the processing chamber will be inclined to disadvantageously flow predominantly through the portion of the gap having the widest spacing, resulting in process non-uniformity across the width of the substrate. Additionally, variations in the distance between the substrate and the top of the processing chamber will typically result in process non-uniformity in plasma enhanced processes. As the intensity of the plasma formed between the substrate and the top of the processing chamber is dependent on the strength of the electrical field defined between the substrate support and the top of the processing chamber, which in turn is dependent on the distance between the substrate support and the top of the processing chamber. If this distance is not uniform, the plasma will not be uniform across the width of the substrate support and will contribute to process non-uniformity. Additionally, in the extreme cases, if the plane of the substrate support is not orientated perpendicular to the center line of the chamber, the plane of a wafer supported thereon may be skewed relative to the plane of operation of a transfer robot utilized to transfer the substrate to and from the processing chamber. In such instances, the end effector of the transfer robot may inadvertently collide with the substrate, causing particular generation and possibly knocking the substrate out of alignment. Moreover, if the lift pin mechanism is not parallel with the substrate support, the lift pins utilized to space the substrate from the substrate support may not extend uniformly through the substrate support, thereby causing the substrate to be supported in a skewed position that may lead to damage during transfer with the transfer robot as described above.
Typically, most substrate supports are coupled to their lift mechanisms by a mechanism in a manner that allows for the plane of the substrate support to be adjusted perpendicular to the center line of the processing chamber. However, many of the adjustment mechanisms utilized to level the substrate support are difficult to secure in a desired position. Furthermore, most adjustment mechanisms do not provide against drift during the securing procedures that is detrimental to systems requiring close parallelism tolerancing.
FIG. 8 depicts one embodiment of a conventional clamping arrangement 800 that is commonly utilized in a processing chamber 820 to couple a substrate support 810 to a lift mechanism 816. The clamping arrangement 800 typically has a clamp block 802 having a hole 804 disposed therethrough. The hole 804 accepts a shaft 806 extending from a lower portion of a stem 808 supporting the substrate support 810. Thus, as the orientation of the shaft 806 within the clamp block 806 is adjusted, the angle of the plane of the substrate support may be adjusted about the center line of the shaft 806.
A disadvantage of such a clamping arrangement 800 is that a clamp screw 812 utilized to clamp hole 804 around the shaft 806 imparts a tangential force upon the shaft 802, thus exerting a rotational moment upon the substrate support 810 as shown by arrow 814. Thus, as the substrate support 810 is being clamped into position, the clamping force, tangential to the shaft 806, causes the parallelism of the substrate support 810 to disadvantageously draft away from a predefined, desired position.
Therefore, there is a need for an apparatus for controlling the position of a substrate support.